An addition-reaction curable silicone rubber composition that contains silicon-bonded hydrogen atoms and silicon-bonded alkenyl groups and is curable by a hydrosilylation reaction in the presence of a hydrosilylation catalyst is known in the art. The above composition can be easily handled and can be cured at a lower temperature and during a shorter time than a radical-reaction curable silicone rubber composition and therefore finds application for manufacturing parts used in office-automation equipment, automobiles, and in other fields of industry. However, when the parts formed from the aforementioned composition operate over long time under conditions of high compression stress, they develop high compression set. In order to reduce these deformations, the aforementioned parts have to be subjected to secondary heat treatment, and this creates significant obstacles for improvement of productivity.
Heretofore, several compositions that contain various organic compounds aimed at the solution of the above problem have been proposed. For example, it was proposed to use an organopolysiloxane rubber composition curable by an addition reaction and compounded with a phthalocyanine compound (see Japanese Unexamined Patent Application Publication (hereafter referred to as “Kokai”) H3-146560 (equivalent to U.S. Pat. No. 5,153,244)). However, articles molded from an organopolysiloxane rubber composition curable by an addition reaction and compounded with a phthalocyanine compound have limited practical application because of coloration caused by the phthalocyanine.
Furthermore, Kokai 2006-56986 (equivalent to US2006-0040116A1) discloses a two-part liquid type curable silicone composition that contains a triazole-based compound or an amidazole-based compound and that is characterized by low compression set. However, triazole-type compounds, such as benzotriazole, are characterized either by extremely slow speed of curing of silicone rubber compositions of the type curable by addition reaction, or by an unpleasant odor emitted during thermal molding of the aforementioned composition.